<body>
<script>
var canvas = document.createElement('canvas');
canvas.width = 500;
canvas.height = 500;
canvas.style.width = '100px';
canvas.style.height = '100px';
var ctx = canvas.getContext('2d');
ctx.filter = 'drop-shadow(0px 50px black)';
ctx.fillStyle = '#0f0';
ctx.fillRect(125, 125, 250, 200);
document.body.appendChild(canvas);
</script>
</body>